This application is based on Patent Application No. 11-129406(1999) filed May 11, 1999 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an optical switch for use in an optical communication system or the like for routing or switching an optical path, and is particularly effective in application to a large-scale matrix optical switch.
2. Description of the Related Art
A variety of optical switches have been proposed, in which a refractive index-matching liquid with a refractive index substantially equal to that of the optical waveguides is sealed in slits formed at crossing points of crossing optical waveguides and moved to switch optical paths at the crossing points of the optical waveguides.
For example, the optical switch disclosed in Japanese Patent Application Laid-open No. 9-133932 (1997) has m optical waveguides not crossing one another in a substrate and n optical waveguides not crossing one another therein, wherein the m optical waveguides cross the n optical waveguides. This optical switch further includes slits each having wall surfaces inclined at a predetermined angle relative to optical axes of these optical waveguides and means (micro heaters) each provided at a corresponding one of the crossing points for generating heat near the corresponding slit. An optically transparent liquid having a refractive index approximate to the refractive index of the optical waveguides is sealed in a part of each of the slits. This optical switch switches optical paths by allowing the micro heaters to generate heat to move the liquid within the slits.
FIG. 1 is an electric wiring diagram of a conventional optical switch according to the above publication.
One element 31 in the illustrated matrix comprises two micro heaters 32a, 32b connected in series to different diodes 33a, 33b, and the two series circuits are connected in parallel so that one of the diodes has a polarity opposite to the other diode. One of two common connected nodes of each series circuit is connected to an upper layer wiring, while the other common connected node is connected to a lower layer wiring.
In addition, Japanese Patent Application Laid-open No. 10-73775 (1998) discloses a method for assembling the optical switch proposed by the above publication. Specifically, as shown in FIG. 2, a silica-based optical waveguide layer 22 is formed on a substrate 21 made of silicon, and a thin metal film such as titanium or chromium with relatively high resistance and another thin metal film such as gold with low resistance are deposited on the optical waveguide layer 22, utilizing the sputtering method or the vacuum evaporation method. Then, a combined method of a photolithography process and a dry etching process is used for treating both the thin films to produce micro heaters 26, electric wirings 25, and a slit, and a silicon layer is then deposited on the optical waveguide layer 22. Subsequently, a substrate 27 made of Pyrex Glass (trade mark) is bonded to the silicon layer with anodic bonding so as to cover the slit, thereby forming a slit 24 at a crossing point between optical waveguides 23. On the other hand, an injection path 29 is formed in a bonding surface of the optical waveguide layer 22 or the substrate 27. Thus, the optical switch according to the above publication is obtained by precisely injecting an appropriate amount of refractive index-matching liquid 31 into the slit 24, through an injection port 30 of the injection path 29 by a method such as pressure control and then blocking the injection port 30 with epoxy resin or the like.
In applying such a conventional optical switch to a large-scale optical matrix switch, the following problems occur.
The above matrix requires at least two micro heaters 26 in one element of the matrix switch. That is, the at least two micro heaters 26 are required to move the refractive index-matching liquid 31 within one slit 24. Since three electric wirings 25 are required to independently supply power to the micro heaters 26 of one element, (2n+1) electric wirings 25 are required for an optical switch comprising n elements arranged in a single row even if a common wiring is used as grounds for the micro heaters 26. Furthermore, (2n+1)xc3x97m electric wirings 25 are required for an (nxc3x97m) optical switch with n elements arranged in m rows.
In addition, to form the optical matrix switch on an electric circuit board, together with a drive circuit for the micro heaters 26 or another circuit mounted thereon, electric wirings 25 of the optical switch must be arranged on an end surface of the optical waveguide layer 22 so that the electric wirings 25 of the optical switch and electric wirings of the electric circuit board can be connected together utilizing the wire bonding method or the like. Thus, the electric wirings 25 must be arranged in such a manner that sufficiently large intervals are provided between the elements, significantly increasing in size of the optical switch. Consequently, it is difficult to manufacture the electric wirings 25 or the like utilizing a combined method of photolithography and dry etching.
In addition, in the above optical switch, to arrange nxc3x97m elements on the optical waveguide layer 22 and to form an injection port 30 corresponding to each slit 24 in each of the side wall surfaces of the substrate 27, large intervals are required between the elements and each slit must be covered by anodically bonding a plurality of substrates 27 together, thereby requiring a large amount of time and labor for manufacturing. On the other hand, to form an injection port 30 corresponding to each slit 24 in a top surface of the substrate 27, injection ports 30 penetrating the optical waveguide layer 22 in a fashion corresponding to optical waveguides 23 formed at a pitch of 250 xcexcm must be densely formed in a substrate 27 of thickness 0.3 mm, for which anodic bonding can be easily carried out. Consequently, formation of the injection ports 30 is very difficult even with dry etching or the micro blasting method. Then, if the thickness of the substrate 27 is reduced to facilitate manufacturing, the substrate 27 may be broken during anodic bonding.
On the other hand, in supplying power to the micro heaters 32a, 32b in FIG. 1, power consumption may increase rapidly according to increasement in wiring length due to the augmented scale of the switch.
As another problem, current may leak at wirings other than those leading to the desired micro heaters or at other micro heaters, thereby preventing power from being supplied only to the desired micro heaters for the purpose of driving the liquid. This problem grows serious as the switch scale enlarges.
In addition, if the above optical switch has an nxe2x89xa0m matrix configuration, the leakage current differs between a row direction and a column direction, whereby other micro heaters may be heated to cause the switch elements to malfunction. Even without the malfunction of the switch elements, the leakage current may disadvantageously vary the optical characteristics of the optical switch.
The present invention provides an optical switch that can solve these problems, and it is a first object of the present invention to provide an optical switch that facilitates size reduction while improving productivity even if it is of a matrix type.
It is a second object of the present invention to provide an optical switch that can efficiently supply power to desired micro heaters while reducing power consumption.
It is a third object of the present invention to provide an optical switch that can prevent malfunctions and variations in optical characteristics caused by leakage current even if it has an nxe2x89xa0m matrix configuration.
It is a fourth object of the present invention to provide an optical switch that can eliminate the adverse effects of leakage current.
The present invention accomplishes an optical switch comprising a plurality of elements arranged in each of a row and a column direction thereof, each of the elements comprising slit located at corresponding crossing point between an optical waveguide extending to a row direction and an optical waveguide extending to the column direction, heating means, provided near each of the slit, with a predetermined resistance value, and liquid with predetermined optical characteristics which moves within the slit depending on heat generated by the heating means. The liquid is moved to switch optical paths at the crossing point between the optical waveguides. The optical switch comprises first electric wirings connecting the heating means of the elements in the same row direction together in condition that a ratio of the resistance value of each heating means to the predetermined resistance value has a predetermined value or smaller, second electric wirings connecting the heating means of the elements in the same column direction together in condition that a ratio of the resistance value of each heating means to the predetermined resistance value has a predetermined value or smaller, and an insulating layer interposed between the first electric wirings and the second electric wirings.
Furthermore, the present invention accomplishes an optical switch comprising a plurality of elements arranged in each of a row and a column direction thereof, each of the elements comprising slit located at corresponding crossing point between an optical waveguide extending to a row direction and an optical waveguide extending to the column direction, a pair of heating means provided near each of the slit, and liquid with predetermined optical characteristics which moves within the slit depending on heat generated by either of the pair of heating means. The liquid is moved to switch optical paths at the crossing points between the optical waveguides. The optical switch comprises a first series circuit having first backflow prevention means connected to one of the pair of heating means, a second series circuit having second backflow prevention means connected to the other of the pair of heating means, first electric wirings connected to the first and second series circuits in common in the same row direction, second electric wirings independently connected to the first and second series circuits in the same column direction, and an insulating layer interposed between the first electric wirings and the second electric wirings.
Furthermore, the present invention accomplishes an optical switch comprising a plurality of elements arranged in each of a row and a column direction thereof, each of the elements comprising slit located at corresponding crossing point between an optical waveguide extending to a row direction and an optical waveguide extending to the column direction, heating means provided near each of the slit, and liquid with predetermined optical characteristics which moves within the slit depending on heat generated by the heating means. The liquid is moved to switch optical paths at the crossing point between the optical waveguides. The optical switch comprises main injection paths each formed between adjacent the elements to the row or column direction of the element and having opposite ends in communication with an exterior and sub injection paths each having one end in communication with a corresponding one of the slit in the element, and the other end in communication with a portion of the main injection path which is nearest to the slit.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.